Edit mbed_targets.md

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Author: Amanda Butler

docs/reference/configuration/mbed_targets.md

@@ -194,22 +194,19 @@ Enabling `is_disk_virtual` adds delay after flashing firmware binary to make sur
 
 The `supported_toolchains` property is the list of toolchains that support a target. The allowed values for `supported_toolchains` are `ARM`, `uARM`, `ARMC5`, `ARMC6`, `GCC_ARM` and `IAR`.
 
-There are few rules and tools behavior you should be aware of when using `ARM`, `ARMC5`, `ARMC6` for `supported_toolchains` as follows.
-* If you specify `ARMC5` in `supported_toolchains`, it means the target supports `Arm Compiler 5 (version 5.06 update 6)` only and the build system will use `Arm Compiler 5` when you specify `-t ARM` or `-t ARMC5` with `mbed compile` command. 
+When using `ARM`, `ARMC5`, `ARMC6` for `supported_toolchains`, please note:
 
-* If you specify `ARMC6` in `supported_toolchains`, it means the target supports `Arm Compiler 6 (version 6.11)` only and the build system will use `Arm Compiler 6` when you specify `-t ARM` or `-t ARMC6` with `mbed compile` command.
+- If you specify `ARMC5` in `supported_toolchains`, it means the target supports Arm Compiler 5 (version 5.06 update 6) only, and the build system uses Arm Compiler 5 when you specify `-t ARM` or `-t ARMC5` with `mbed compile` command. 
 
-* If a target specify `ARM` in `supported_toolchains`, it means the target supports compiling with both `Arm Compiler 5` and `Arm Compiler 6`. Note that starting with `MbedOS 5.12 release`, `Arm Compiler 6` will 
-be the default ARM Compiler for MbedOS. So, for a target which specifies `ARM` in `supported_toolchains`, the system will default to using `Arm Compiler 6` when you specify `-t ARM` with `mbed compile` command. If the build system
-fails to detect a valid configuration for `Arm Compiler 6`, it will automatically(without any manual intervention) try to detect if a valid confguration for `ARM Compiler 5` exists, and will continue using `ARM Compiler 5` if it successfully detects `ARM Compiler 5`. You may see a warning message in your standard output from build system indicating this behavior. 
+- If you specify `ARMC6` in `supported_toolchains`, it means the target supports Arm Compiler 6 (version 6.11) only, and the build system uses Arm Compiler 6 when you specify `-t ARM` or `-t ARMC6` with `mbed compile` command.
 
-* You can only specify one of `ARM`, `ARMC5` or `ARMC6` for `supported_toolchains` for a target in `targets/targets.json` or `custom_targets.json`.
+- If you specify `ARM` in `supported_toolchains`, it means the target supports compiling with both Arm Compiler 5 and Arm Compiler 6. Arm Compiler 6 is the default Arm Compiler for Mbed OS. If a target specifies `ARM` in `supported_toolchains`, the system defaults to using Arm Compiler 6 when you specify `-t ARM` with `mbed compile` command. If the build system fails to detect a valid configuration for Arm Compiler 6, it automatically (without any manual intervention) tries to detect if a valid confguration for Arm Compiler 5 exists and continues using Arm Compiler 5 if it successfully detects Arm Compiler 5. You may see a warning message in your standard output from the build system indicating this behavior.
 
-* It's invalid to specify `-t ARMC5` with `mbed compile` command for a target that specifies `ARMC6` for `supported_toolchains` or vice-versa.
+- You can only specify one of `ARM`, `ARMC5` or `ARMC6` for `supported_toolchains` for a target in `targets/targets.json` or `custom_targets.json`.
 
-<div style="background-color:#F3F3F3; text-align:left; vertical-align: middle; padding:15px 30px;"> 
-Note: Please note that Arm Compiler 6 is the default Arm Compiler for Mbed OS development. Most Mbed OS platforms are already compatible with Arm Compiler 6. Some existing targets still supporting Arm Compiler 5 will be migrated to Arm Compiler 6 in the future. Please be aware that you must use Arm Compiler 6 for future development as Arm Compiler 5 support will be deprecated in future.
-</div>
+- It's invalid to specify `-t ARMC5` with the `mbed compile` command for a target that specifies `ARMC6` for `supported_toolchains` or vice-versa.
+
+<span class="notes">**Note:** Arm Compiler 6 is the default Arm Compiler for Mbed OS development. Most Mbed OS platforms are already compatible with Arm Compiler 6. Some existing targets still supporting Arm Compiler 5 will be migrated to Arm Compiler 6 in the future. Please be aware that you must use Arm Compiler 6 for future development because Arm Compiler 5 support will be deprecated in September 2019.</span>
 
 #### default_toolchain