Material progress specific variables

`$mt-progress-background-color`

Type: color

Default value: $theme-primary-faded-background-color

Computed value: #bbdefb

`$mt-progress-color`

Type: color

Default value: $theme-primary-emphasis-background-color

Computed value: #1e88e5

`$mt-progress-alternate-color`

Type: color

Default value: $theme-primary-background-color

Computed value: #1976d2

`$mt-progress-height`

Type: size

Default value: $4px

Computed value: 4px